Pelagic deep-sea metazoan biodiversity and ecology revealed by environmental DNA analysis in combination with other censuses

The deep sea (> 200 m) not only represents the largest habitat on earth, but also has the highest faunal biomasses and greatest number of individual organisms. While the deep sea provides humans with substantial services, its ecosystems remain poorly studied. Logistical and technical challenges to sample deep-sea ecosystems as well as organisms’ avoidance behavior to underwater gear stress the need for alternative techniques. In this thesis, I focused on a relatively novel tool in deep-sea biology; environmental DNA (eDNA) analysis. Environmental DNA is genetic material that organisms shed into their environment. This eDNA can be assigned to a specific taxon and provides information on species presence, diversity and distribution without the need to encounter or capture the source animal. The first objective of this thesis was to develop a pipeline to collect diversity and distribution data on deep-sea cephalopods with eDNA analysis from water and sediment samples. The second objective was to establish biodiversity baselines and distribution patterns of key organisms in the deep sea and to put these patterns into an ecological context. The third objective of this thesis was to identify cephalopod and fish taxa that potentially contribute to the vertical transport of carbon. This thesis showed that eDNA can be used successfully in the assessment and monitoring of deep-sea pelagic metazoans in hotspots of diversity and climate change. Especially when eDNA analysis is analyzed in different kinds of samples and used in combination with other techniques, it can help to answer ecological questions and ultimately contribute to aid in conservation of deep-sea habitats.